Process of manufacturing a free machining case-hardening steel



Patented May 9, 1939 UNITED STATES PATENT OFFICE PROCESS OF MANUFAC GAFREE TURIN MACHINING CASE-.HARDENING STEEL poration No Drawing. Application June 15, 1937,

- Serial No. 148,324

16 Claims.

, This invention relates to a new free machining open hearth steel having properties not heretofore developed in such steels, and to a process for manufacturing the same. In the lower carbon ranges, the new steel has the properties of a case hardening steel having high ductility and tensile strength. In the higher carbon ranges, the new steel is suitable for heat treatment. This application is a continuation in part of my application, Serial No. 70,11 filed March 21, 1936. In the past, most open hearth and Bessemer free machining steels have been produced by increasing the sulphur and manganese content above that of the average commercial open hearth steel, the silicon and phosphorus content remaining about the same. For free machining case hardening steels the manganese content is often run as high as 1.20% and sometimes even to 1.50% with a sulphur content often of 0.20%

and sometimes 0.30% as compared to manganese contents of 0.60% and 0.80% and sulphur content below 0.05% in ordinary steels. Such steels commonly carry a phosphorus content of about 0.04% and one commercial Bessemer steel of this type has a phosphorus range of from 0.09% to 0.13%. Their silicon content is usually in the range of ordinary steels and is not generally specified in the S. A. E. specifications since heretofore it has been considered of small importance. Such steels are free machining steels capable of case hardening but have the disadvantage of being non-uniform and sometimes brittle. This lack of uniformity and brittleness is caused by the formation .of manganese sulphide in isolated masses known commercially as segregations and which weaken the 'bars at the points where they occur. Heretofore these segregations have been considered an inescapable evil accompanying the high sulphur and manganese content which has been found advantageous in producing a steel capable of machining at high speeds.

Heretofore the freest machining steels have been vthose known as SAE X1112, SAE 1112 5 and SAE X1314 in the low carbon range and SAE 1040 in the higher carbon ranges. SAE X1112 and SAE 1112 have the best machining qualities but are rather brittle Bessemer steels having poor ductility and poor case hard- 50 ening properties. SAE X1314 is fairly good tom the standpoint of free machining and case hardening but has a low yield point. Its ductility, while better than X1112 and 1112, is still rather poor. As compared with these steels, the steel 55 produced in accordance with this invention in the same carbon range has superior machinability, much better ductility, superior case hardening properties and a much higher yield point. In, case hardening it produces a harder, deeper case in less time and with much less warpage. 5

In the higher carbon range, SAE 1040 has a good compensated ductility but is relatively poor from the standpoint of free machining. The new steel in this range has substantially the same ductility characteristics as SAE 1040 but has a 10 machinability rating which compares favorably with that of the low carbon steels.

Heretofore no free machining steel having a high compensated ductility rating has been manufactured. Steel produced in accordance 15 with this invention up to 0.55% carbon has machinability rating of at least 80, compared to SAE 1112 taken as 100. In addition its compensated ductility rating is higher than any other free machining steel. The compensated 20 ductility of steels produced hereunder'is above 28 and generally of the order of 31--33. Compensated ductility (hereinafter referred to as D-C rating) is calculated according to the following formula: 25

D-C rating=E+0.43C

TX YXEXM loll where T is the ultimate tensile strength in pounds per square inch, Y the yield point in 40 pounds per square inch, E the elongation percentage in 2", M the machinability based upon MCS rating= SAE 1112.as 100, and C is the carbon content of the steel expressed in hundredths of 1%. T, Y, E and M are based on cold drawn material.

Steel produced in accordance with this invention has an MCS rating of at least 140 and normally about 150. This compares with an MCS rating of 113 for X1112, 89 for 1112 and 102 for x1314. Ridgely .15% carbon steel produced hereunder had an MCS rating 01- approximately 217.

Steel produced hereunder has a yield point of at least 75,000 lbs. based on a 1" rod.

My invention contemplates producing a steel having sulphur and manganese contents sumciently high to permit cutting speeds as high or higher than present steels but in which the excessive formation of manganese sulphide which produces segregation is reduced to a minimum. According to my invention, the sulphur is believed to form soluble iron sulphides which are uniformly distributed throughout the heat and in turn throughout the ingot, billet and bar and which add materially to the free machining quality of the steel. This result is accomplished by reducing the silicon and phosphorus content. which has heretofore been considered unimportant, to a commercial minimum, by the method of control of the manganese and sulphur content hereinafter described, and by rolling the steel within critical temperature ranges. Each of these four factors contributes to the reduction of manganese sulphide segregations.

The preferred specification of my new steel is as follows:

Phosphorus 0.02 maximum 3112mm 0.02 maximum The steel may be made with carbon contents from 0.08 to 0.75% or higher, the lower carbon steel having excellent case hardening characteristics and the higher carbon steel having heat treating properties. Departure from these preferred specifications, within the usual commercial tolerances, may. be made without extremely deleterious results.

It is important that the phosphorus and silicon content be kept as low as possible. More phosphorus or silicon than that specified above reduces the amount of sulphur and manganese which can be absorbed by the steel without producing segregations. Less silicon and prosphorus permits more manganese and sulphur to be used. The manganese and sulphur contents should be in the ratio of about 5 to 1.

In the manufacture of the steel by my new process, the furnace is preferably charged with pig ironand scrap steel or with scrap steel alone,

open hearth practice being followed in this respect. The amount of manganese added at this point should not be sufficient to cause appreciable segregations of manganese sulphide. Ordinarily the amount of manganese present in the furnace is well below l%--say .84 to .9l%.

The charge is preferably poured from the furnace at the usual pouring temperature of approximately 2850" F. and is allowed to stand in the ladle until it has cooled approximately F. or more. In the case of a charge sufilcient to pour 1'75 tons of ingots this cooling requires approximately 30 minutes. At the end of the desired cooling time, a further addition of ferro-manganese is made sufficient to bring the final manganese content to the desired amount. Free sulphur is also added at the same time if the sulphur contents of the original charge and tor in reducing the formation of manganese sulthe added term-manganese does not give the desired final sulphur contents.

The additions in the ladle still further lower the temperature of the heat but not sumclently to permit solidification before pouring of the in- 5 sets can be completed.

The addition of the last portion of manganese and sulphur at a reduced temperature as in the ladle appears to be an extremely important facl0 phide segregations. Apparently, at this reduced temperature, the reaction forming manganese sulphide does not take place to so great a degree as at the higher temperature, if at all. Furthermore, the time required to solidify from the lower temperature is so much less than from the higher temperature that such manganese sulphide as may possibly be formed does not have sufficient time to segregate before the charge has solidifled in the ingot mold.

After the ingots have solidified, the molds are stripped and the ingots placed in the soaking pit and held at about 2460 F. until ready to roll. The rolling from ingot to billet is done with the least possible temperature drop. The billets, cut to proper length. are then reheated for the rolling from billet to bar.

In the rolling of bars of the low carbon steel from the billets, the starting temperature is about 2400 F. and the finishing temperature is kept as high as possible. Preferably at about 1860 F. to 1880" F. Below this finishing temperature it is found that cracks, seams and segregations occur which destroy in a large degree the desirable properties of the steel. For the high carbon steel the critical rolling temperatures are much lower, the preferable starting temperature being below 2100" F. Higher rolling temperatures for the high carbon steel produce a porous steel having incorrect density and excessive scale.

When used'for case hardening, the new steel carburizes to the same depth in less time and gives a harder case and tougher core than other carburizing steels, and is uniform and free from brittleness. One of its most important characteristics is its freedom from excessive warpage. This characteristic is so marked that it may be used for parts, such as relatively long pins with ground journals on each end, which cannot be made from other case hardening steels. This propertyis due in a large measure to the uniformity of the material.

The following table indicates the relative properties of steel made according to the present invention and contain other steels, referring only to these steels in the cold drawn state:

SAE x1112 200 to 235 to SAE lll2 150 100 94 SAE 1010 115 00 Ridgcly 0.18 carbon 190 to 210 120 Ridgely 0.39 ear- 65 bon 100 I05, 750 81,000 it. 5 4 48-56 Ridgely 0.47 carbon l40tol50 90133008234013 2.556-65 Column AMachining speeds in it. per min.

Column B-Machinabllity rating. Column C-Tensile strength, pounds per sq. in. (0

Column D-Yield point, pounds per sq. in. Column Fl-Percent elongation in 2. Column F-'lorsion tests, 360 turns in i2" Column G-Impact test, it.-lbs.

The figures given for Ridgely steels are conservative averages. 7|

Steel produced according to the present invention not only machines more readily than comparable steel. but machines in an entirely ,smoother appearance and texture than surfaces machined in the same manner with other steels.

Another important result of the new steel is increased tool life. It has been found in practice that tools used in machining the new steel may be used several times as long as with other free machining steels notwithstanding greater cutting speeds.

While the invention is particularly applicable to steels having no other metallic contents than heretofore mentioned, it may be used with steels containing small amounts of other metallic elements such as nickel, chromium, molybdenum, vanadium, etc. When so used, it produces a steel having superior machinability to steels of the same class.

The term "free machining as used in the claims means a machinability rating of the order of or better for steels having 0.55% carbon or less and correspondingly lower ratings for the higher carbon steels.

The invention claimed is:

1. The process of manufacturing a free machining steel comprising adding to afused mass of steel containing insufllcient manganese and sulphur to form substantial segregations of manganese sulphide, material of the group of materials consisting of manganese and sulphur, in an amount suflicient normally to form segregations of manganese sulphide, the addition being carried out at a temperature approximately 25002600- F.. whereby no substantial segregations of manganese sulphide are formed.

2. The process of manufacturing a free machining steel comprising adding to a fused steel charge containing less than 1% manganese, sufficient material of the group of materials consisting of manganese and sulphur to produce a manganese content of at least 1% and a sulphur content of at least 20%, the addition being carried out at a temperature approximately 2500- 2600 F.

3. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur and pouring the charge into a ladle at approximately 2850" F., cooling the charge at least 100 F., after pouring and then adding more manganese and sulphur in the ladle, the charge and additions being proportioned to give a steel having at least 1.0% manganese and .18% sulphur.

4. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur and pouring the charge into a ladle at approximately 2850 F., cooling the charge at least 100 F. after pouring and then adding more manganese and sulphur in. the ladle, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur, approximately 70% of the necessary manganese being added in the first addition and 30% in the second addition.

5-. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur and pouring the charge into a ladle at approximately 2850 F., cooling the charge after pouring and adding more manganese and sulphur before solidification, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur.

6. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur and pouring the charge into a ladle at approximately 2850 F., cooling the charge after pouring and adding more manganese and sulphur before solidification, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur, approximately 70% of the necessary manganese being added in the first addition and 30% in the second addition.

7. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur at or above the region of 2850 F., cooling the charge and adding more manganese and sulphur before solidification, the charge and additions being proportioned to give a steel hav: ing at least 1.00% manganese and .18% sulphur.

8. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur at or above the region of 2850 F., cooling the charge and adding more manganese and sulphur before solidification, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur, approximately 70% of the necessary manganese being added in the first addition and 30% in the second addition.

9. The process of manufacturing a free machining steel, comprising the steps of melting a charge in an open hearth furnace with lime as a flux in the proportion of about 8% of the charge, adding manganese and sulphur at or above the region of 2850" F., cooling the charge and adding more manganese and sulphur before solidification, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur.

10. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with lime as a flux in the proportion of about 8% of the charge, adding manganese and sulphur and pouring the charge into a ladle at approximately 2850 F., cooling the charge at least 100 F., after pouring and then adding more manganese and sulphur in the ladle, the charge and addition being proportioned to give a steel having at least 1.00% manganese and .18% sulphur.

11. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with lime as a flux in the proportion of about 8% of the charge,

adding manganese and sulphur and pouring the charge into a ladle at approximately 2850 E, cooling the charge after pouring and adding more manganese and sulphur before solidification, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur, approximately 70% of the necessary manganese being added in the first addition and 30% in the second addition.

12. The process of manufacturing a free machining steel comprising the steps'of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below 02%, adding manganese and sulphur at or above the region of 2850 E, cooling the charge and adding more manganese and sulphur before solidification, the charge and addition being proportioned to give a steel havthe charge into ingots and rolling fromingots to billets, reheating the billets to approximately 2400" F. and rolling from billets to bars all of the latter rolling taking place at or above the region of 1850 1".

13. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur at or above the region of 2850' F., cooling the charge and adding more manganese and sulphur before solidification, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur and approximately 30% to .50% carbon, forming the charge into ingots and rolling from ingots to billets, reheating the billets and rolling from billets to bars all of said latter rolling taking place with a starting temperature below 2100 R, and a finishing temperature 'in the region of 1650 I".

14. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace, adding manganese and sulphur, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur and approximately .08% to carbon, forming the charge into ingots and rolling from ingots to billets, reheating the billets to approximately 2400 F. and rolling from billets to bars all of the latter rolling taking place at or above the region of 1850 F.

15. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace, adding manganese and sulphur, the charge and additions being proportioned to give a steel having at least 1.00% manganese and .18% sulphur and approximately 30% to .40% carbon, forming the charge into ingots and rolling from ingots to billets, reheating the billets and rolling from billets to bars all of the latter rolling taking place with a starting temperature below 2100 1". and a finishing temperature in the region of 1650' I".

16. The process of manufacturing a free machining steel comprising the steps of melting a charge in an open hearth furnace with a basic flux to reduce the phosphorus and silicon contents each below .02%, adding manganese and sulphur at or above the region of 2850' F., cooling the charge and adding more manganese and sulphur before solidification, the charge and addition being proportioned to give a steel having a carbon content of approximately .08% to 50% and a sulphur content of at least .18% and manganese in the amount of approximately five times the sulphur, forming the charge into ingots and rolling from ingots to billets, reheating the billets to a rolling temperature, and rolling from billets to bars, all of the latter rolling being carried out at a temperature above 1650" to 1850 F., the higher temperature corresponding to the lower carbon contents and vice versa.

JAMES A. RIDGELY. 

